During a refueling operation, liquid fuel is supplied to the tank of a motor vehicle. Fuel vapors which are present in the fuel tank are displaced by the liquid fuel filling the tank and must be properly vented in order to prevent an undesirable pressure build-up. It is preferable that such venting takes place in response to the initiation of the refueling operation rather than waiting for the vapor pressure to increase to a high level. Thus, it has been known in the art to provide venting arrangements which operate in response to the insertion of a fuel nozzle. Examples of such arrangements are disclosed in U.S. Pat. Nos. 4,765,504, 4,630,749, and 4,719,949.
However, the arrangements disclosed in these patents are all directed to constructions in which the mouth of the system is sealed with a removable cap. The use of a removable cap can often times be problematic due to the potential for loss by the operator. When the cap is lost and the system is not properly sealed, debris can enter the system and fuel vapors escape.
Typically during operation of a motor vehicle, fuel in the fuel tank will be consumed so as to create a vacuum condition. In order to alleviate this vacuum condition, typical fuel systems allow ambient air to be drawn into the fuel tank. In order to facilitate air flow, a removable fuel cap may be configured to provide for such flow or one or more orifices may be formed in the filler neck. However, the air permitted to flow into the fuel tank is unfiltered and can carry with it debris and contaminants. Such unfiltered air can have a harmful effect on the fuel's purity and can result in decreased vehicle performance. Furthermore, if the removable fuel cap is lost, even more debris will be permitted into the refueling system when the flap valve door opens inwardly because the cap is not present to prevent debris from entering the mouth of the system.